Exterior ballistic software is widely known and used for accurately predicting the trajectory of a bullet, including ballistic drop and other ballistic phenomena. Popular software titles include Infinity 5™, published by Sierra Bullets, and PRODAS™, published by Arrow Tech Associates, Inc. Many other ballistics software programs also exist. Ballistics software may include a library of ballistic coefficients and typical muzzle velocities for a variety of particular cartridges, from which a user can select as inputs to ballistic calculations performed by the software. Ballistics software typically also allows a user to input firing conditions, such as the angle of inclination of a line of sight to a target, range to the target, and environmental conditions, including meteorological conditions. Based on user input, ballistics software may then calculate bullet drop, bullet path, or some other trajectory parameter. Some such software can also calculate a recommended aiming adjustment that would need to be made in order to hit the target. Aiming adjustments may include holdover and holdunder adjustments (also referred to as come-up and come-down adjustments), designated in inches or centimeters at the observed range. Another way to designate aiming adjustment is in terms of elevation adjustment to a riflescope or other aiming device (relative to the weapon on which the aiming device is mounted), typically expressed in minutes of angle (MOA). Most riflescopes include adjustment knob mechanisms that facilitate elevation adjustments in ¼ MOA or ½ MOA increments.
For hunters, military snipers, SWAT teams, and others, it is impractical to carry a personal computer, such as a laptop computer, for running ballistics software. Consequently, some shooters use printed ballistics tables to estimate the amount of elevation adjustment necessary. However, ballistics tables also have significant limitations. They are typically only available for level-fire scenarios in ideal conditions or for a very limited range of conditions and, therefore, do not provide an easy way to determine the appropriate adjustments for aiming at inclined targets, which are elevated or depressed relative to the shooter.
Methods have been devised for using level-fire ballistics tables in the field to calculate an estimated elevation adjustment necessary for inclined shooting. The most well known of these methods is the so-called “rifleman's rule,” which states that bullet drop or bullet path at an inclined range can be estimated as the bullet path or bullet drop at the corresponding horizontal range to the elevated target (i.e., the inclined range times the cosine of the angle of inclination). However, the rifleman's rule is not highly accurate for all shooting conditions. The rifleman's rule and other methods for estimating elevation adjustment for inclined shooting are described in the paper by William T. McDonald titled “Incline Fire” (June 2003).
Some ballistic software programs have been adapted to operate on a handheld computer. For example, U.S. Pat. No. 6,516,699 of Sammut et al. describes a personal digital assistant (PDA) running an external ballistics software program. Numerous user inputs of various kinds are required to obtain useful calculations from the software of Sammut et al. '699. When utilizing ballistic compensation parameters calculated by the PDA, such as holdover or come-up, a shooter may need to adjust an elevation setting by manually manipulating an elevation adjustment knob of the riflescope. Alternatively, the user may need to be skilled at holdover compensation using a riflescope with a special reticle described by Sammut et al. '669. Such adjustments may be time consuming and prone to human error. For hunters, the delay involved in making such adjustments can mean the difference between making a shot and missing an opportunity to shoot a game animal.
The present inventors have identified a need for improved methods and systems for ballistic compensation that are particularly useful for inclined shooting and which would also be useful for archers.